By "roasted zinc sulphide concentrates" is meant the product obtained by roasting a zinc sulphide bearing concentrate. The term zinc calcine is also used to refer to such products. Typically, roasted zinc sulphide concentrates contain zinc oxide and other components, including zinc sulphate, zinc sulphide, mixtures of metal oxides such as copper, lead, calcium, cadmium, and magnesium, zinc ferrite, magnetite, and possibly some haemetite. Aqueous ammoniacal ammonium carbonate solutions are used to selectively leach zinc from roasted zinc sulphide concentrates, leaving a substantial portion of the iron components in the leach residue.
Ammoniacal ammonium carbonate solutions have been suggested for treating zinc scrap and mini-steel plant baghouse dusts to recover zinc oxide. However, it was not previously known that such solutions could be used to leach roasted zinc sulphide concentrates, which are dissimilar to zinc scrap and baghouse dust, to produce such high quality, high surface area zinc oxide as are obtained by this invention. Zinc oxide with the high specific surface area produced by this invention can be classed as premium zinc oxide.